1. Field of the Invention
The present invention relates to a technique of image shooting using a microscope, and more particularly to a technique of automatic exposure used in shooting.
2. Description of the Related Art
With an image shooting apparatus provided with an automatic exposure function using brightness information of an image that is currently being observed with a microscope, a suitable brightness cannot normally be attained by once executing an automatic exposure process which therefore needs to be repeatedly executed.
With weak fluorescence microscopy, an exposure time increases in order to obtain an image of a suitable brightness due to a sample being dark. This leads to a problem in that a display update speed (frame rate) slows down because of an increase in the convergence time of an automatic exposure if the image of the sample is displayed live.
As a technique for obtaining an image of suitable brightness in photomicroscopy, a variety of methods have been proposed.
For example, Patent Document 1 (Japanese Laid-open Patent Publication No. 2003-185931) discloses a microscope including an LED light source and a brightness adjustment knob thereof. With the microscope disclosed by Patent Document 1, by operating the adjustment knob, the brightness of the LED light source can be pulse-controlled in synchronization with a driving pulse of a CCD (Charge Coupled Device), and the brightness of a subject can be adjusted.
Additionally, Patent Document 2 (Japanese Laid-open Patent Publication No. 2002-290803) discloses a system for increasing an output gain of a CCD when a dark sample is shot. With the system disclosed by Patent Document 2, the gain is set to a large value so as not to have noticeable noise because unnecessarily increasing the gain degrades image quality, an aperture is opened, and an exposure time is increased so as to make up for insufficient brightness, whereby a suitable exposure is obtained.
With this system, a display update speed (frame rate) of a live image slows down due to an increase in the exposure time, and the image is not immediately updated even though the orientation, the posture, a zoom magnification, or the like of a digital camera is changed. Therefore, the system according to Patent Document 2 is provided with a cancel button for canceling an exposure.
Furthermore, Patent Document 3 (Japanese Laid-open Patent Publication No. 2005-221708) discloses a photomicroscopy apparatus that makes up brightness by adjusting an illumination, and controls insufficient brightness by increasing the amount of amplification of a gain in order to implement a comfortable frame rate while suppressing degradation in image quality of even a dark sample to a minimum.